As prior-art solid cosmetic materials containing moisture, water-in-oil emulsions containing liquid oil, solid oil, water, and a lipophilic surfactant are generally used (e.g., Patent Document 1). However, water-in-oil emulsions pose a problem that electrolytes, particularly water soluble or hydrophilic substances that exert physiological functions when applied to the skin, cannot exhibit the functions effectively. This is because, in water-in-oil emulsions, the aqueous phase in which the electrolyte as an active ingredient is dissolved is enclosed by the oil phase and therefore it is difficult to bring the electrolyte into contact with the skin.
In contrast, oil-in-water emulsions have, on the exterior, an aqueous phase in which an electrolyte having physiological functions is dissolved, which improves the permeability of the electrolyte in the skin. Thus, such electrolytes having physiological functions are preferably formulated into oil-in-water emulsions as solid preparations. Heretofore, solid compositions comprising an oil-in-water emulsion are already known. For example, the following are reported: solid cosmetics comprising an oil-in-water emulsion having a surfactant, oil, and β-1,3-glucan (Patent Document 2); solid cosmetics comprising an oil-in-water emulsion having water, specific wax ester, an amphoteric surfactant, titanium oxide of a specific shape, and higher fatty acid (Patent Document 3); solid cosmetics comprising an oil-in-water emulsion having agar and/or gelatin, polyethylene glycol, an oil, and water (Patent Document 4).
However, oil-in-water emulsions are disadvantageous in that when the electrolyte is dissolved in the aqueous phase, the emulsion cannot form a gel, which results in that the emulsion cannot solidify or cannot maintain sufficient hardness. In addition, in some case, oil-in-water emulsions have another disadvantage that physiological functions of an electrolyte dissolved in the aqueous phase cannot be sufficiently exhibited. The above-described disadvantages are obvious particularly when a purine base, its salt, or a water soluble vitamin is used as an electrolyte. The inventors confirmed that the disadvantages tend to become prominent particularly when a specific amount of purine base or its salt is used in combination with a specific amount of water soluble vitamin.
In the present circumstances, since the above-described disadvantages have not been overcome, practical use of solid compositions comprising an oil-in-water emulsion having an effective concentration of electrolyte with physiological functions has not yet been achieved. In view of the above-described prior-art techniques, it has been demanded to develop solid compositions comprising an oil-in-water emulsion that have sufficient hardness and good feel when used, and can sufficiently exhibit the physiological functions of an incorporated electrolyte.    [Patent Document 1] Japanese Unexamined Patent Publication No. H6 (1994)-321731    [Patent Document 2] Japanese Unexamined Patent Publication No. H8 (1996)-291021    [Patent Document 3] Japanese Unexamined Patent Publication No. H9 (1997)-194331    [Patent Document 4] Japanese Unexamined Patent Publication No. 2003-95862